Muon-catalyzed fusion
Muon-catalyzed fusion is a process that allows fusion at room temperature. Although it does allow for fusion, it does not currently provide anywhere close to breakeven energy. It is sometimes known as cold fusion although this term is no longer often used as it can create confusion with other scientifically unestablished forms of room temperature fusion.In muon-catalyzed fusion, deuterium and tritium nuclei form atoms with muons, which are essentially heavy electrons. The muons orbit very close to the nuclei, shielding the positive charge of the nuclei so the nuclei can move close enough to fuse.
The main problem with muon-catalyzed fusion is that muons are unstable, and hence, there needs to be some cheap means of producing muons, and the muons so produced must be arranged to catalyze as many reactions as possible before decaying. As J.D. Jackson recognized in his seminal 1957 paper, "Catalysis of Nuclear Reactions between Hydrogen Isotopes by Mesons," Physical Review, Vol. 106, No. 2, April 15, 1957, the real problem with muon-catalyzed fusion is that there is a non-vanishing probability (about 1%, actually) that the muon would "stick" to the particle (a Helium-4 nucleus) that results from the deuterium and tritium fusion, removing the muon from the catalysis process. Even if the muon were absolutely stable, it could only catalyze about 100 fusions before sticking, about a factor of 5 too few to provide breakeven energy.
See also
nuclear fusion, Antimatter catalyzed nuclear pulse propulsion